EP1563196A1

EP1563196A1 - Improved friction bearing for hydraulic machines and hydraulic machine equipped with said bearing

Info

Publication number: EP1563196A1
Application number: EP02793323A
Authority: EP
Inventors: Gabriele Pecorari
Original assignee: SAI Societa Apparecchiature Idrauliche SpA
Current assignee: SAI Societa Apparecchiature Idrauliche SpA
Priority date: 2002-11-18
Filing date: 2002-11-18
Publication date: 2005-08-17
Also published as: WO2004046572A1; CN1701185A

Abstract

The friction bearing for hydraulic machine (5) comprising a surface in contact and sliding on the surface of the crank, the said surface is carried out on an element inserted (4) in ferrous material interposed between said crank (10) and the piston (9) or its connecting rod (8), there is also a layer inserted in anti-friction plastic material (3) anchored solidly on this by a layer in sintered metal (2), and has a layer of anti-friction plastic material with a minimum thickness (3) but which is slightly greater than the maximum dimension of the particles not captured by the filter of the hydraulic circuit where the hydraulic machine is inserted ; it also has the thickness of the element in ferrous material (1) of said bearing between 0.4 and 4 % of the sliding diameter on the hub (6) of the crank (10). The principal operation, standardization, and dimension reduction advantages, compared to the prior art, are also illustrated.

Description

IMPROVED FRICTION BEARING FOR HYDRULIC MACHINES AND HYDRAULIC MACHINE EQUIPPED WITH SAID BEARING

The invention concerns an improved friction bearing for hy- draulic machines, more advantageously with radial cylinders, and a hydraulic machine equipped with said bearing, that is a special configuration of the support device of the thrusts between the crank and the pistons which slide on the former, to generate or receive the torque from the drive shaft; in particular for bear- ings used in high-speed rotating hydraulic machines which require the reduction of the overall dimensions of the machine.

Prior art includes various types of friction bearings, hydrostatic sliding on the crank or oscillating on a ring interposed between these pistons and the rotating bearing on the crank. Nevertheless, the adoption of rolling-contact bearings is not always possible because it makes the crank cumbersome and the hydraulic machine is consequently overly big in proportion to the displacement. Thus, only the use of friction bearings makes it possible to keep down the overall dimensions of the machine.

Prior art further includes the use of bearings made of higher resistance plastics; among these materials the following have proven suitable: laminated phenolic plastic (HDV of DIN stan- dards), KEVLAR (brand name) or also VESPEL (brand name manufactured by Dupont); layers of polyetheretherketone (PEEK) or MELDIN (brand name manufactured by Furon) have also been used with equal results; these latter have been used in thin layers anchored by a layer of sintered foam metal.

The excessive variety of materials which can be used and the sometimes difficult assessment of the load conditions which characterize the thrust contact between the piston and the crank in said hydraulic machines, even if mediated by the connecting rods with which certain types of machines are equipped, lead to an in- finite number of possible solutions, and thus to an excessive amount of time required to test them all, and to the adoption of combinations of materials, thicknesses and arrangements which limit the applicability of the resulting hydraulic machine; both due to the imperfect resistance to the elevated loads of the above- mentioned friction bearings made entirely of plastic, because they are subject to become very hot, as well as due to the elimination of the heat and the englobing capacity of the metal particles present in the hydraulic liquid, because very frequently insuffi- ciently or, on the contrary, excessively sized to the purpose.

Another solution known in the prior art, for the sliding of the shoes of the pistons on the hub of the crank of hydraulic machines, is to make in the shoe a hydraulic balancing bearing, the size of the shoe is conveniently 80-90% of the area of the piston to which it is connected; it follows that varying the dimensions of the piston and therefore of the displacement of the hydraulic machine, the hydraulic balancing surface must also be varied in order to modify the dimensions of the hydraulic machine by the greatest diameter of the piston employed and therefore by the most space required by these accessory parts, at the expense of- the overall dimensions of the machine.

In hydraulic machines, particularly radial cylinder hydraulic machines, the elevated loads that the pistons transmit to the drive shaft make it necessary to adopt the use of rolling-friction bearings, with a considerable increase of the outside dimensions of the machine with regards to the displacement, or to the use of the above mentioned friction bearings choosing from among the var- ious combinations known and proposed by the prior art.

Finally, prior art includes the technique of using shoes made of a material which is softer than the sliding surface on the hub; in any case the particles which are not trapped by the filter, be- cause smaller than the filtering capacity of the same, become em- bedded and remain imprisoned in the said soft material of the shoe grating on and damaging the surface of the hub on which they are rubbed by the said shoe, even if this use surface has a hardness of 60 HRc.

Said prior art is susceptible to additional improvements with regards to the possibility of finding a definitive and high-efficiency, as well as extremely economical, configuration which makes it possible to carry out the said anti-friction plain bearings which carry out the optimum operation with regards to the impurities and to the elimination of the heat generated in the process of sliding.

From the above ensues the need to solve the technical problem of finding a conformation to the said friction bearing which, in addition to being easily produced in large quantities, accomplishes the best compromise of the opposing technical demands indifferently to the presence of the particles suspended in the hydraulic liquid, not captured by the filtering device used, and simultane- ously accomplishes a sufficient elimination of the heat generated in the process of sliding even if this -bearing is positioned on a thin element inserted in the contact zone between the crank and the piston or its connecting rod.

The invention solves the above-mentioned technical problem, adopting: a friction bearing for hydraulic machines, comprising a surface in contact and sliding on the surface of the crank, the said surface is carried out on an element inserted in ferrous material interposed between said crank and the piston or its con- necting rod, there is a layer inserted in anti-friction plastic material anchored solidly on this by a layer in sintered metal, characterized by this, which has a layer in anti-friction plastic - material with a minimum thickness but which is slightly greater than the maximum dimension of the particles not captured by the filter of the hydraulic circuit where the hydraulic machine is in- serted; has in addition the thickness of the element in ferrous material of this bearing between 0.4 and 4% of the sliding diameter on the hub of the crank.

Adopting, in a further and preferred embodiment: the hardness of the slide surface of the hub of the crank at the minimum value of 80 HRc.

Adopting, in a second preferred embodiment: the thickness of the said layer of anti-friction plastic material between 1/100 and 12/100 of a millimeter; and the thickness of the said layer of anchorage sintered metal between 10/100 and 40/100 of a millimeter.

Adopting, in a further and preferred embodiment: the said antifriction plastic material made of polyetheretherketone (PEEK) .

Adopting, in a further and preferred embodiment: the thickness of the said layer of anti-friction plastic material between 8/100 and 9/100 of a millimeter.

Adopting, in a further and preferred embodiment: the thickness of the said layer of anchorage sintered metal between 21/100 and 23/100 of a millimeter. Adopting also, in a successive embodiment: the thickness of the said element in interposed ferrous material between 12/10 and 13/10 of a millimeter excluding the thickness of the anti-friction plastic material layer and the anchoring sintered layer.

An embodiment of the invention is illustrated simply by way of example, in the two drawings attached hereto, in which Figure 1 is a partial section of the friction bearing according to the invention; Figure 2 is a schematic longitudinal cut-away view of a radial cylinders hydraulic machine with connecting rods in which it is very convenient to use the bearing in the contact between the shoe of the connecting rod and the surface of the crank; Figure 3 is a schematic transverse cut-away of the hydraulic machine in Figure 2; Figure 4 is the plan view of an element interposed between the said shoe of the connecting rod and the surface of the crank; Figure 5 is the section V-V of Figure 4. Figure 1 shows the layers of the interposed ferrous element 1, on which is present the sintered layer 2 for the anchorage of the layer of anti-friction plastic material 3. This element 4 intend- ed collectively is interposed in the hydraulic machine 5, of Figure 2, between the hub 6 and the base 7 of the connecting rod 8, to connect the corresponding piston 9 to crank 10.

Figure 4 shows the tubs 11 to anchor the said interposed element 4 to the base 7 of the connecting rod 8 to carry out the thrust R on the surface of the said hub 6, the lubrication hole 12 is also visible.

Tests conducted demonstrate that the best. results were obtained utilizing an element interposed in ferrous material with a thick- ness of 12/10 of a millimeter, to which was applied the layer of anchorage sintered metal with a thickness of 23/100 of a millimeter, as well as the layer of anti-friction plastic material PEEK with a thickness of 8/100 of a millimeter. Said elements mounted on a radial cylinder hydraulic machine with connecting rods, like the one illustrated, allowed the use of the same shoe, that is interposed element 4, for a large variety of diameters of the piston connected to this; in other words it was possible to vary the displacement, and consequently the characteristics of the hydraulic machine, modifying only the bore values of the cylinder. The filter employed had the usual filtering capacity of 60 μm, that is with the maximum dimension of the particles released equal to 6/100 of a millimeter, in other words slightly less than the thickness of the layer of PEEK. The hub 6 had a 90 mm slide diameter of the shoe. After many hours of operation the slide surface of the hub 6 of the crank 10 did not show signs of grooving typical of the anti-friction shoes known in the prior art.

The advantages obtained with this invention are: hydraulic machines, advantageously with radial cylinders, have highly stan- dardized accessory parts and show a reduced increase of the over- all dimensions with the increase of the displacement, in order to permit the production of high-performance hydraulic machines, but at lower costs. In addition, the adoption of the anti-friction plastic material PEEK is advantageous due to the low friction co- efficient and due to the limited thickness of this layer to permit the neutralization of the effect of the contamination particles of the hydraulic liquid,"but simultaneously to easily release the heat generated in the friction on the hub.

In practice, the materials, dimensions and certain details may be different from the ones indicated, but they are technically equivalent and therefore do not go beyond the legal scope of this invention.

Claims

1. Friction bearing for hydraulic machines (5), comprising a surface in contact and sliding on the surface of the crank, in which the said surface is carried out on an element inserted (4) in ferrous material interposed between said crank (10) and the piston (9) or its connecting rod (8), there is a layer inserted in anti-friction plastic material (3) anchored solidly on this by a layer in sintered metal (2), characterized in that it has: the thickness of the layer in anti-friction plastic material (3) with a minimum thickness which is nevertheless slightly greater than the maximum dimension of the particles not captured by the filter of the hydraulic circuit where the hydraulic machine is inserted; has in addition the thickness of the element in ferrous material (1) of this bearing between 0.4 and 4% of the sliding diameter on the hub (6) of the crank (10).

2. Friction bearing for hydraulic machine, according to the previous claim, characterized in that it has the hardness of the sliding surface of the hub (6) of the crank (10) at the minimum value of -80 HRσ.

3. Friction bearing for hydraulic machine, according to one of the previous claims, characterized in that it has the thickness of the said layer of anti-friction plastic material (3) between 1 and 12/100 of a millimeter; and the thickness of the said layer of anchorage sintered metal (2) between 10/100 and 40/100 of a millimeter.

4. Friction bearing for hydraulic machine, according to one of the previous claims, characterized in that it has the said antifriction plastic material made of polyetheretherketone (PEEK) .

5. Friction bearing for hydraulic machine, according to previous claim 3 characterized in that it has the thickness of the said layer of anti-friction plastic material (3) between 8/100 and 9/100 of a millimeter.

6. Friction bearing for hydraulic machine, according to previous claim 3 characterized in that it has the thickness of said layer of anchorage sintered metal (2) between 21/100 and 23/100 of a millimeter.

7. Friction bearing for hydraulic machine, according to one of the previous claims, anchorage sintered metal the thickness of the said element in interposed ferrous material (1) between 12/10 and 13/10 of a millimeter excluding the thickness of the layers of anti-friction plastic material anti-friction and anchorage sintered metal.

8. Radial cylinders hydraulic machine characterized in that it has in the contact between the sliding surface of the shoe of the relative hydraulic cylinder on the crank, the interposition of an inserted element equipped with an anti-friction bearing in plastic material carried out according to one or more of the previous claims from 1 to 7.